Liquid pavement marking compositions

ABSTRACT

A pavement marking composition, methods of applying, and pavement markings produced therefrom. The composition is a two-part coating composition having an amine component including one or more aspartic ester amines and optionally one or more amine-functional coreactants, an isocyanate component including one or more polyisocyanates, and material selected from the group of fillers, extenders, pigments, and combinations thereof.

This is a continuation of application Ser. No. 09/096,923 filed Jun. 12,1998 now U.S. Pat. No. 6,166,106 that claims the benefit of U.S.Provisional Application No. 60/049,572, filed Jun. 13, 1997.

BACKGROUND OF THE INVENTION

There is a significant need for a liquid pavement marking compositionthat will provide increased durability and retained reflectivity onceapplied to a surface and dried or cured. Compositions of this type aretypically used on roads, highways, parking lots, and recreationaltrails, to form stripes, bars and markings for the delineation of lanes,crosswalks, parking spaces, symbols, legends, and the like. They aretypically applied by spray coating (i.e., painting) the pavementsurface. Preformed pavement marking sheets or tapes have also been usedto mark pavement or traffic bearing surfaces.

Pavement marking stripes, or pavement markings of other shapes, mayinclude reflective optical elements adhered to the pavement surface bythe use of a binder. Current traffic paint systems typically useconventional 1.5 n_(η) glass microspheres for retroreflection. Themicrospheres are typically flood coated onto the wet marking immediatelyafter coating. This provides the paint with improved retroreflectivityand also covers the top surface of the uncured or undried coating with aprotective layer of microspheres. This protective layer allows themarkings to be exposed to traffic sooner because of the layer ofmicrospheres over the surface, which prevents transfer of the coating tothe surface of vehicle tires. This is important for rates of markingapplication. The time between application and the point where materialwill no longer transfer to vehicle tires is defined as the “track-free”time. Shorter track-free times increase marking efficiency by reducingor eliminating the need for traffic disruption through such measures asclosing lanes or placing traffic control devices to protect suchmarkings.

It would be advantageous to apply markings in a wider range of weatherconditions than is possible with existing compositions. There is also aneed for marking compositions with improved cure profiles to ensure bothsubstrate wet out and rapid track-free time. Furthermore, improvementsare needed to obtain compositions that are substantially free ofvolatile organic components.

SUMMARY OF THE INVENTION

The present invention provides a pavement marking including a binderhaving polyurea groups. Conventional liquid pavement markingcompositions include alkyd-based binder compositions as described inU.S. Pat. No. 2,897,732 (Shuger), U.S. Pat. No. 2,897,733 (Shuger), andU.S. Pat. No. 3,326,098 (Boettler), and epoxy-based compositions asdescribed in U.S. Pat. No. 4,088,633 (Gurney), U.S. Pat. No. 4,185,132(Gurney), and U.S. Pat. No. 4,255,468 (Olson). Such conventionalcompositions are not desirable for at least one of the followingreasons: they typically dry too slowly; they need elevated temperaturesfor reasonable cure times; they contain chemical linkages (e.g., esterlinkages) that are susceptible to degradation (as by hydrolysis, forexample); and/or they require the use of organic solvents, drying oils,or drying accelerators, which can lead to discoloration.

Numerous other conventional pavement marking compositions have beendeveloped to get faster dry times by using heated application ofmaterials to road surfaces. Also, waterborne coatings based on acryliclatices, as disclosed in U.S. Pat. No. 5,527,853 (Landy et al.), andepoxy resin emulsions, as disclosed in U.S. Pat. No. 4,906,716(Cummings), have been suggested for use in pavement markings. Suchmarkings do have the advantages of low volatile organic content and onepart coating compositions, but they are not yet sufficiently durable forlong term road presence and retained reflectivity performance.

U.S. Pat. No. 4,076,671 (Bright) discloses a resinous composition saidto be useful for marking trafficable surfaces. The two part acrylatebased coating compositions are said to provide a desirable balance ofstability and fast cure, but require the use of free monomers and lowmolecular weight ethylenically unsaturated compounds which havesignificant vapor pressures. Also, they require the use of peroxidecatalysts. U.S. Pat. No. 5,478,596 (Gurney) discloses liquid pavementmarking compositions prepared from a two part polyurethane-formingsystem of a first component having isocyanate-reactive groups (a polyol)and a second component having isocyanate groups.

A need exists for liquid pavement marking compositions that can provideone or more, and preferably all, of the following features: reducedenvironmental impact through formulations having low volatile organiccontent; improved balance of coating rheology during application andfilm formation to promote substrate wet out and fast cure to track-freefilms; broadened range of weather conditions for coating application;and/or improved marking performance through increased durability andretained reflectivity. To achieve one or more, and preferably all, ofthese features, the present invention provides a pavement markingincluding a binder having polyurea groups.

Pavement markings of the present invention preferably include a binderhaving polyurea groups, wherein the binder is prepared from a coatingcomposition comprising one or more aliphatic secondary amines, one ormore polyisocyanates, material selected from the group of fillers,extenders, pigments, and combinations thereof, and reflective elements(e.g., glass beads, etc.). Preferably, the pavement marking has aretained reflectivity of at least about 100 mcd/m²/lux after at leastabout 2 years in use as longitudinal traffic markings as measuredaccording to ASTM E 1710-95. Preferably, the binder is prepared from atwo-part coating composition comprising an amine component comprisingone or more aspartic ester amines and optionally one or moreamine-functional coreactants, and an isocyanate component comprising oneor more polyisocyanates. A traffic bearing surface having thereon such apavement marking is also provided.

Also provided is a pavement marking that includes a binder havingpolyurea groups, wherein the binder is prepared from a sprayable,two-part coating composition substantially free of volatile organiccomponents and comprising an amine component comprising one or moreaspartic ester amines and an isocyanate component comprising one or morepolyisocyanates. At least one of the amine component and/or theisocyanate component further comprises material selected from the groupof fillers, extenders, pigments, and combinations thereof. The coatingcomposition has a minimum application temperature of at least about 7°C. and a track-free time of no greater than about 5 minutes. A trafficbearing surface having thereon such a pavement marking, and a pre-formedpavement marking wherein the pavement marking is coated on a substratethat can be applied to a traffic bearing surface are also provided.

The present invention also provides coating compositions. In oneembodiment, the coating composition includes one or more aliphaticsecondary amines, one or more polyisocyanates, and material selectedfrom the group of fillers, extenders, pigments, and combinationsthereof. The coating composition has a minimum application temperatureof at least about 7° C., a track-free time of no greater than about 5minutes, and forms a pavement marking having reflective elements with aretained reflectivity of at least about 100 mcd/m²/lux after at leastabout 2 years in use as longitudinal traffic markings as measuredaccording to ASTM E 1710-95.

Also provided is a sprayable two-part liquid pavement markingcomposition comprising an amine component comprising one or moreaspartic ester amines and optionally one or more amine-functionalcoreactants, and an isocyanate component comprising one or morepolyisocyanates. The amine component, the isocyanate component, or bothfurther comprise material selected from the group of fillers, extenders,pigments, and combinations thereof. The coating composition is sprayableand has a minimum application temperature of at least about 7° C. and atrack-free time of no greater than about 5 minutes. Preferably, thepavement marking composition comprises an amine component comprising oneor more aspartic ester amines and optionally one or moreamine-functional coreactants, and an isocyanate component comprising oneor more polyisocyanates.

Methods of applying such compositions are also provided. For example, amethod of marking a traffic bearing surface is provided. This methodincludes providing an amine component comprising one or more asparticester amines and optionally one or more amine-functional coreactants,providing an isocyanate component comprising one or morepolyisocyanates, providing material selected from the group of fillers,extenders, pigments, and combinations thereof in either the aminecomponent, the isocyanate component, or both, combining the aminecomponent and the isocyanate component to form a coating compositionhaving a minimum application temperature of at least about 7° C., and atrack-free time of no greater than about 5 minutes, spraying the coatingcomposition onto a traffic bearing surface, and applying reflectiveelements to the composition coated on the traffic bearing surface toform a pavement marking.

Another embodiment includes a method of preparing a pavement marking.This method includes providing an amine component comprising one or morealiphatic secondary amines, providing an isocyanate component comprisingone or more polyisocyanates, providing material selected from the groupof fillers, extenders, pigments, and combinations thereof in either theamine component, the isocyanate component, or both, combining the aminecomponent and the isocyanate component to form a coating compositionhaving a minimum application temperature of at least about 7° C., and atrack-free time of no greater than about 5 minutes, applying the coatingcomposition to a surface, and applying reflective elements to thecomposition coated on the surface to form a pavement marking havingreflective elements with a retained reflectivity of at least about 100mcd/m²/lux after at least about 2 years.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pavement marking compositions of the present invention comprise abinder comprising urea groups (—NR—C(O)—NR—). This binder can beprepared from a two-part system that includes an amine component and anisocyanate component. Preferably, the amine component includes primaryor secondary amines. More preferably, the amine component includes oneor more secondary amines, such as an aspartic ester amine, which is analiphatic secondary diamine. Most preferably, the amine componentincludes one or more aspartic ester amines, optionally blended with oneor more amine-functional coreactants other than an aspartic ester amine.Preferably, the amine-functional coreactants are polymeric polyamines,and more preferably, substantially polymeric diamines. Theseamine-functional coreactants are selected to balance the properties ofthe coating during the curing process and in its final form.

The amine and isocyanate components are chosen such that the resultantpavement marking is generally resistant and durable to environmental andvehicular stresses and has good daytime visibility. Preferably, it alsohas good night-time visibility. Durability can be evidenced by goodadhesion to a wide variety of substrate surfaces, including concrete,asphalt, and other markings, whether they be markings of the same ordifferent material. It can also be evidenced by good adhesion (oftenreferred to as “anchoring”) of reflective elements to the marking, ifthey are used. As used herein, “durability” can be determined byapplying the pavement marking to a road surface that will be exposed totraffic conditions and monitoring the performance of the marking overtime. Reflectivity and whiteness can be measured instrumentally in thefield and the resistance of the marking to wear and erosion can besubjectively evaluated. Durable markings have continued adhesion to thesubstrate, good visibility, and, preferably, good reflectivity over anextended length of time.

The pavement markings formed from the composition of the presentinvention preferably are durable (i.e., have a useful life) for at leastabout 2 years, more preferably, for at least about 3 years, and mostpreferably, for at least about 4 years in use as longitudinal trafficmarkings. If reflective elements are used, the pavement markings have aretained reflectivity of at least about 100 mcd/m²/lux, and morepreferably, at least about 150 mcd/m²/lux, throughout their useful lifeas longitudinal traffic markings. As used herein, “retainedreflectivity” is used to describe the effectiveness of maintainedretroreflective performance of a pavement marker over its useful life.Retroreflectivity is currently typically measured by a portableinstrument in the field at fixed entrance and observation angles,according to ASTM E 1710-95. Recent work (Transportation Research Record1409 published 1994 by the Transportation Research Board) has shown thatthe entrance angle at which light is incident and observation anglesfrom which a driver actually views a pavement marking, referred toherein as “approximate driver geometries,” are appropriate for measuredretroreflective performance of pavement markings.

The amine and isocyanate components are preferably chosen such that theresultant pavement marking composition: (1) is a liquid with a highsolids content, which is substantially free of volatile organiccomponents (preferably, less than about 5 wt-% volatile organiccomponents, typically solvents, based on the total weight of thecomposition); (2) has a generally rapid cure profile, with a track-freetime (i.e., a dry time at ambient roadway conditions when the coating isapplied) of preferably, no greater than about 5 minutes, morepreferably, no greater than about 4 minutes, and most preferably, nogreater than about 3 minutes), and a useful open time (i.e., the lengthof time the composition will remain in a liquid state after applicationto a surface) for adequate substrate wet out and particle or reflectiveelement wicking/anchorage (preferably, an open time of at least about 30seconds, and more preferably, at least about 1 minute); (3) has a broadapplication window (i.e., it is able to be applied over a wide range oftemperatures), with emphasis on use at lower temperatures (preferably,having a minimum application temperature of at least about 7° C., morepreferably, at least about 4° C., even more preferably, at least about2° C., and most preferably, at least about −4° C.); (4) is compatiblewith two part static mix or airless high pressure impingement-mixapplication equipment; (5) includes commercially available, low cost rawmaterials; and (6) is generally storage stable (preferably, having auseful shelf-life of at least 6 months, more preferably, at least oneyear, and most preferably, at least two years). As used herein, avolatile organic component (VOC) is an organic compound with a vaporpressure of more than 0.01 mm Hg (13.33 Pascals) at 20° C. Suchcompounds typically have a boiling point of greater than 250° C.

The pavement marking compositions of the present invention comprise abinder comprising urea groups (—NR—C(O)—NR—), although other groups mayalso be present, such as biuret groups (—NR—C(O)—NR-C(O)—NR—),isocyanurate groups

as well as urethane groups (—NR—C(O)—O—), and the like, where R is ahydrogen or an organic group. Such polymers containing urea groups areoften referred to herein as polyureas. Polyureas formulated for pavementmarking applications should be resistant to abrasion and provideadhesion to road surfaces and reflective elements.

The binder system is the reaction product of an amine with an isocyanateto form a urea linkage. Preferably, the binder system is the reaction ofa polyaspartic ester amine, which is preferably difunctional, with apolyisocyanate to form a polyurea.

Preferred aspartic ester amines have the following formula

wherein R¹ is a divalent organic group (preferably, having 1-40 carbonatoms), and each R² is independently an organic group inert towardisocyanate groups at temperatures of 100° C. or less.

In the above formula, preferably, R¹ is an aliphatic group (preferably,having 1-40 carbon atoms), which can be branched, unbranched, or cyclic,and more preferably, R¹ is selected from the group of divalenthydrocarbon groups obtained by the removal of the amino groups from1,4-diaminobutane, 1,6-diaminohexane, 2,2,4- and2,4,4-trimethyl-1,6-diaminohexane,1-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane,4,4′-diamino-dicyclohexyl methane or3,3-dimethyl-4,4′-diamino-dicyclohexyl methane. Divalent hydrocarbongroups obtained by the removal of the amino groups from relatively highmolecular weight polyether polyamines containing aliphatically boundprimary amino groups, such as the products marketed under the tradedesignations “JEFFAMINE” by Texaco and Huntsman, and “HYCAR” by B.F.Goodrich, are also suitable. Other suitable polyamine precursors includeethylene diamine, 1,2-diaminopropane, 2,5-diamino-2,5-dimethylhexane,1,11-diaminoundecane, 1,12-diaminododecane, 2,4- and/or2,6-hexahydrotoluylene diamine, and 2,4′-diamino-dicyclohexyl methane.Aromatic polyamines such as 2,4- and/or 2,6-diaminotoluene and 2,4′-and/or 4,4′-diaminodiphenyl methane are also suitable but lesspreferred.

In the above formula, preferably, each R² is independently an organicgroup having 1-40 carbon atoms, more preferably, each R² isindependently an alkyl group (preferably, having 1-20 carbons), whichmay be branched or unbranched, and most preferably, each R² isindependently a lower alkyl group (having 1-4 carbon atoms).

Suitable aspartic ester amines are commercially available from Bayer(Pittsburgh, Pa.) under the trade designations “DESMOPHEN” XP-7053,XP-7059, and XP-7109, for example.

“DESMOPHEN” XP-7053 is substantially composed of the following compound:

“DESMOPHEN” XP-7059 is substantially composed of the following compound:

“DESMOPHEN” XP-7109 is substantially composed of the following compound:

For particularly advantageous results, one or more amine-functionalcoreactants can be used in addition to the aspartic ester amines. Theseamines (other than aspartic ester amines) typically function as chainextenders and/or impact modifiers. The use of such an amine-functionalcoreactant can contribute to the presence of soft segments in thepolymer backbone for improved toughness properties. They can be primaryamines, secondary amines, or combinations thereof. Preferably, they aresecondary amines, a blend of secondary amines, or a blend of secondaryamines and primary amines. Some primary amines tend to react so rapidlythat they are useful only in small quantities or in combination with avery slowly reacting isocyanate, such as m-tetramethylxylenediisocyanate (TMXDI). In some instances, a significant amount of primaryamines can be used, and the overall coating cure rate can be moderatedor slowed down with the use of a slower aspartic ester amine, such as,for example, “DESMOPHEN” XP-7053. Most preferably, the amine-functionalcoreactant comprises a secondary amine.

The amine-functional coreactant is preferably an amine-terminatedpolymer. Examples of such polymers include, but are not limited to,those available from Huntsman Chemical, under the trade designation“JEFFAMINE” polypropylene glycol diamines such as “JEFFAMINE” D-2000,those available from B.F. Goodrich, Cleveland, Ohio, under the tradedesignation “HYCAR” ATBN (amine-terminated acylonitrile butadienecopolymers), and those disclosed in U.S. Pat. No. 3,436,359 (Hubin etal.) and U.S. Pat. No. 4,833,213 (Leir et al.) (amine-terminatedpolyethers, and especially polytetrahydrofuran diamines).

A wide variety of polyisocyanates may be utilized in preparing thebinder of the present invention. “Polyisocyanate” means any organiccompound that has two or more reactive isocyanate (—NCO) groups in asingle molecule. Particularly useful polyisocyanates can be aliphatic,alicyclic, or a combination thereof. This definition includesdiisocyanates, triisocyanates, tetraisocyanates, etc., and mixturesthereof. Most preferably, aliphatic isocyanates, includingcycloaliphatic isocyanates, are used to improve weathering and diminishyellowing.

Useful polyisocyanates include, but are not limited to, those selectedfrom the group consisting of bis(4-isocyanatocyclohexyl)methane (H₁₂MDI,available from Bayer Corp., Pittsburgh, Pa.), diphenylmethanediisocyanate (MDI, available from Bayer Corp., Pittsburgh, Pa.),isophorone diisocyanate (IPDI, available from Huels America, Piscataway,N.J.), toluene 2,4-diisocyanate (TDI, available from Aldrich ChemicalCo., Milwaukee, Wis.), hexamethylene diisocyanate (HDI, available fromAldrich Chemical Co., Milwaukee, Wis.), m-tetramethylxylene diisocyanate(TMXDI, available from Aldrich Chemical Co., Milwaukee, Wis.), and1,3-phenylene diisocyanate. Mixtures of polyisocyanates can also beused. Furthermore, while monomeric isocyanates could be useful, they arenot preferred, but could be used to make adducts and prepolymers thatwould be preferred.

Preferred polyisocyanates include derivatives of the above-listedmonomeric polyisocyanates. These derivatives include, but are notlimited to, polyisocyanates containing biuret groups, such as the biuretadduct of hexamethylene diisocyanate (HDI) available from Bayer Corp.,Pittsburgh, Pa. under the trade designation “DESMODUR” N-100,polyisocyanates containing isocyanurate groups, such as that availablefrom Bayer Corp., Pittsburgh, Pa. under the trade designation “DESMODUR”N-3300, as well as polyisocyanates containing urethane groups, uretdionegroups, carbodiimide groups, allophonate groups, and the like. Thesederivatives are preferred as they are polymeric and have very low vaporpressures and negligible free isocyanate monomer.

There are many useful commercially available adducts of the monomericisocyanates. There are also many useful adducts and prepolymers that arenot presently commercially available that could be prepared, such as forexample, the reaction products of the above mentioned aspartic esteramines with diisocyanates such as IPDI, TMXDI, and the like.

The stoichiometry of the polyurea reaction is based on a ratio ofequivalents of isocyanate to equivalents of aspartic ester amine andoptional amine coreactant. Preferably, the isocyanate is used in anexcess. More preferably, the isocyanate:amine ratio is less than about1.15:1. Even more preferably, the isocyanate:amine ratio is less thanabout 1.1:1. Most preferably, the isocyanate:amine ratio is less thanabout 1.05:1. The lower ratios of isocyanate to amine can potentiallylead to the formation of a looser polymer network and increasedviscoelastic damping in the cured coating.

To achieve desired stoichiometries, the amine and isocyanate componentsare combined in a volume ratio of preferably about 1:1 to about 5:1amine to isocyanate components. More preferably, the ratio is within arange of about 1:1 to 3:1 amine to isocyanate components. Particularlypreferred ratios are 2:1 and 3:1 amine to isocyanate components.

The pavement marking compositions of the present invention are referredto as two-part systems, containing one or more aspartic ester amines,optionally blended with one or more amine-functional coreactants (otherthan an aspartic ester amine), and one or more polyisocyanates as thetwo component reactive system. Additional components such as variousadditives can be used to achieve desirable results. For example,weathering additives such as UV absorbers, hindered amine lightstabilizers, antioxidants, dispersing and grinding aids, wetting agents,impact modifiers (e.g., rubber tougheners such as those available underthe trade designations “PARALOID” 2691 and EXL-2330 from Rohm and Haas),defoamers, suspension stabilizers, biocides, etc., can be added to thebinder to improve the manufacturability and the overall durability ofmarkings of the present invention. Significantly, however, no catalystsare needed to achieve desirable track-free times.

Also, pigments (e.g., TiO₂), fillers (e.g., talc, CaCO₃, clay, ceramicmicrospheres, hollow polymeric microspheres, and hollow glassmicrospheres), extenders, diluents, plasticizers, leveling agents, andsurfactants can be used. Pigments impart desired visual appearanceproperties in the daytime and contribute to reflective performance ofthe marking at night. Fillers and extenders can be used to modify flowproperties of the liquid coating and contribute to the bulk volume ofthe final coating with lower cost per volume materials. Fillers, such asceramic microspheres, hollow polymeric microspheres (such as thoseavailable under the trade designation EXPANCEL 551 DE from Akzo Nobel,Duluth, Ga.), and hollow glass microspheres (such as those availableunder the trade designation K37 from Minnesota Mining and ManufacturingCo., St Paul, Minn.), are particularly useful and may also be added toachieve a specific volume ratio for the two components of this two-partcoating without significantly affecting the reactive chemistry of thecoating mixture. The pigments, fillers, and extenders can have asignificant impact on uncured formulation and cured film density, filmcure profile and track-free time, cured film modulus, coating adhesionto a substrate, response to thermal cycling, possible shrinkage ofpolymer components, abrasion, and coating durability. Typically at leastabout 15 weight percent of the final dried coating is made up of suchnon-soluble material, more preferably, at least about 20 weight percentand, most preferably, at least about 25 weight percent. In someinstances, about 30 weight percent to about 42 weight percent ofpigments, fillers, and extenders can be used.

A particularly preferred type of filler is hollow glass microspheres.Hollow glass microspheres are particularly advantageous because theydemonstrate excellent thermal stability and a minimal impact ondispersion viscosity and density. They also are rapidly and easilydispersed with low shear mixing and demonstrate relatively littleequipment abrasion. Preferably, the microspheres are incorporated intothe amine component for enhanced storage stability. Field trials haveshown that incorporation of at least about 30 volume percent, andpreferably about 30 volume percent to about 40 volume percent of hollowglass microspheres into pavement marking compositions of the presentinvention result in improved durability of the pavement marking.

The pavement marking compositions of the present invention are typicallyapplied directly to a traffic bearing surface with or without a primerlayer or to a substrate that is applied to the surface. This can be doneusing spray coating techniques. Typically, the amine component and theisocyanate component are applied using a spraying apparatus that allowsthe components to combine immediately prior to exiting the apparatus.For example, two-component, high pressure, airless, impingement mixingsystems can be used. Also, plural component spray equipment with astatic mixer can be used.

An example of an airless, impingement mixing spray system ismanufactured by Gusmer (1 Gusmer Drive, Lakewood, N.J. 08701-0110). Thesystem will include the following components: a proportioning sectionwhich meters the two components and increases the pressure to aboveabout 1500 psi (10.34 MPa); a heating section to raise the temperaturesof the two components (preferably, independently) to control viscosity;and an impingement spray gun which combines the two components andallows mixing just prior to atomization. Other manufacturers ofimpingement systems include Binks Manufacturing (Chicago, Ill.) andGlas-Craft (Indianapolis, Ind.).

Another system useful for applying polyurea coatings is a system whichuses a static mix tube to achieve blending of the two components. Thesystem is similar to that of the impingement unit in that it meters,builds pressure, and heats the components. However, at the spray gun,the components are combined and pumped through a length of tubing whichcontains elements designed to mix the components prior to atomizing.This system requires periodic flushing of the static mix tube to preventaccumulation of cured polyurea which could plug the spray gun. Anexample of such a spray gun is a Binks Model 43P.

Viscosity behavior of the each of the two components is important fortwo part spray coating processes. With impingement mixing, the two partsshould be as close as possible in viscosity at high shear rates to allowadequate mixing and even cure. The plural component static mix/spraysystem appears to be more forgiving of viscosity differences between thetwo components. Characterization of viscosities as functions of shearrate and temperature can help with decisions as to starting point fortemperatures and pressures of the coatings in the two part sprayequipment lines.

The liquid pavement marking compositions of the present inventionprovide polyurea coatings having conventional daytime visibility. Theycan also function as binders to anchor reflective optical elements.Generally, the reflective elements do not exceed about severalmillimeters in diameter. When the reflective elements are glass orceramic microspheres, they are typically in the range of about 200micrometers to about 600 micrometers.

The reflective elements can be in the form of glass beads (also referredto as microspheres or microsphere lenses) that are preferably lighttransmissible. Chemical treatment of bead surfaces, such as with anorganochromium compound, may be utilized as known in the art to enhanceresin to glass adhesion. Other chemical coupling agents such as silanes,titanates and zirconates are also known. Additionally, fluorocarbontreatment of the glass beads can aid in achieving substantially uniformhemispherical bead sinkage.

Post-spray applied elements in the form of glass or ceramic beads ormicrospheres can also be used as a binder filler in addition toproviding night time reflectivity. They may function similarly tomineral particulates on the wear surface of a coated abrasive(sandpaper), protecting the polymeric binder from applied stresses. Themicrosphere average diameter, application or coverage rate (weight perunit area) and surface chemistry (e.g., treatment with coupling agent)affect the durability of pavement markings. Preferably, typical coveragerates correspond to greater than about 4 pounds of glass beads pergallon (479 grams/liter) of binder, more preferably, greater than about10 pounds per gallon (1200 grams/liter). This corresponds to,preferably, greater than about 6 grams glass beads per 300 cm² area, fora 15 mil (0.4 mm) thick cured film, more preferably greater than about15 grams of glass beads per 300 cm² area for a 0.4 mm thick cured film.

The reflective elements can also be in the form of ceramic microspheres(i.e., beads). “Ceramic” is used herein to refer to inorganic materialswhich can be either crystalline (a material having a patterned atomicstructure sufficient to produce a characteristic x-ray diffractionpattern) or amorphous (a material having no long range order in itsatomic structure evidenced by the lack of a characteristic x-raydiffraction pattern). Amorphous ceramics are more commonly known asglasses. Ceramic beads are preferred as they are more durable and moreresistant to wear than are glass microspheres. Prior to the presentinvention, ceramic beads have not been practical to use in paintedpavement markings because the binder has not been sufficiently durableand adherent to roads.

The ceramic beads or other reflective microspheres can be applieddirectly to the binder coated on the pavement surface. Alternatively,they can be applied in the form of retroreflective optical elementshaving vertical surfaces. Vertical surfaces provide better orientationfor retroreflection. Also, they may prevent the build-up of a layer ofwater over the retroreflective surface during rainy weather, whichotherwise interferes with the retroreflection mechanism.

One type of such retroreflective optical elements with vertical surfacesis made up of pellets comprising a thermoplastic core coated withceramic beads. Such reflective elements and methods of making them aredisclosed in the published International Publication No. WO 97/03814(Bescup, et al.). Layered elements have been made using polymers havingdiffering melt behavior. The retroreflective elements include aplurality of optical elements, such as glass or ceramic microspheres,partially embedded in the vertical surfaces of the reflective elementcore's central layer. Such reflective elements and methods of makingthem are disclosed in International Publication No. WO 97/28471.

All-ceramic retroreflective elements can be made, which may be used inpavement markings, with greatly improved resistance to wear and theeffects of weathering. These retroreflective elements are preferablyfree of metals and polymeric material. These retroreflective elementsare comprised of an opacified ceramic core and ceramic optical elementspartially embedded into the core. The opacified ceramic cores of thesecomposite reflective optical elements will often contain a mixture ofamorphous (glass) and crystalline phases. The retroreflective elementmay be irregular in shape or in the form of a sphere, disc, tile, etc.The diffuse reflecting ceramic core, in combination with the transparentoptical elements embedded in the surface, provides a surprisingly brightretroreflective element without the gray coloration and thesusceptibility to corrosion associated with metallic specularreflectors. Such reflective elements and methods of making them aredisclosed in U.S. patent application Ser. No. 08/591,570.

Many other variations of composite retroreflective elements oraggregates are known which have a polymeric core with optical elementsembedded in the core surface. See, for example, U.S. Pat. Nos.3,252,376; 3,254,563; 4,983,458; 4,072,403; 4,652,172; and 5,268,789.Other retroreflective elements can also be constructed having a ceramiccore and glass optical elements with a metallic specular coating. See,for example, U.S. Pat. Nos. 3,043,196; 3,175,935; 3,556,637; 3,274,888;and 3,486,952; and EP Publication No. 0,322,671. Ceramic retroreflectiveelements typically exhibit greater resistance to weathering and to wear.Some known embodiments also contain optical elements dispersedthroughout the core. The core may be irregular in shape or may beregularly shaped e.g., spheres, tetrahedrons, discs, square tiles, etc.Retroreflective elements are advantageous because they can be embeddedinto inexpensive painted markings.

Whatever the type of reflective element, they can be flood coated ontothe entire surface of the binder painted on the pavement surface;however, this can be quite expensive for ceramic microspheres.Alternatively, the reflective elements can be positioned only in themost efficient optical part of the surface. Control of element placementon liquid markings is important for obtaining durable highretroreflectivity. They can also be included within one of thecomponents prior to mixing and applied, for example, during the spraycoating of the two-component liquid.

Also, it is important to understand the mechanism of embedment ofelements, whether in the form of coated pellets or microspheres. Surfacetreatments can be used to obtain appropriate sinkage, not too deep ornot too shallow, and control wetting and capillation of the coating upthe sides of the element. Also, the cure rheology of the two-part bindersystem can affect the ability to sink elements.

The following examples are offered to further illustrate the variousspecific and preferred embodiments and techniques. It should beunderstood, however, that many variations and modifications may be madewhile remaining within the scope of the present invention. For example,the particular materials and amounts thereof recited in these examples,as well as other conditions and details, are to be interpreted to applybroadly in the art and should not be construed to unduly limit theinvention.

EXAMPLES

The following procedure is a typical one useful for preparing the aminecomponent of two-part compositions of the invention.

Pigment Dispersion Procedure

Step 1: In the appropriate size mixing vessel, charge one half or lessby wt of the amine component (preferably the most viscous), and thedispersant, if used. Mix at low shear (500-1000 rpm) for 1 minute toblend. Add TiO₂ pigment, if used, in two portions. Mix with Cowles-typeimpeller blade, at low shear (500-1000 rpm) for several minutes, untiluniform consistency.

Step 2: Add additional extenders (those which are not shear-sensitive)to the mixing vessel in several portions, followed by mixing to avoidclump formation.

Step 3: Once all nonshear-sensitive extenders are added, mix at highshear to disperse agglomerated pigment and extenders. This typicallyrequires use of the appropriate size Cowles-type blade (e.g. 4 inch(10.2 cm) diameter for use in 5 gallon (19 liter) pail), at 2,000-3,000revolutions per minute (rpm), over the course of 20-60 minutes or more.The optimum rpm depends on batch size, viscosity and component types.Additional amine/liquid component can be added as required to maintain aviscosity that is appropriate for grinding.

The batch temperature will increase to 120° F. to 140° F. (49° C. to 60°C.). A Hegman-type grind gauge is used to monitor dispersion progress. Agrind to a particle size of less than one mil was typically achieved,which corresponds to a 7.0 on the PC grind scale.

Step 4: Remaining amine and other liquids are added at this time, withlow shear mixing.

Step 5: Shear sensitive extenders, such as the hollow glass or polymericmicrospheres are added in portions as required to prevent clumping, anddispersed with a low shear blade, such as a propeller or jiffy-stylemixer, and rpms of 500 or less, for 10-15 minutes.

The following materials were used to prepare examples of the presentinvention.

Ingredient Description Supplier Location Amine Component “DESMOPHEN”XP-7109 aspartic ester diamine Bayer Corp. Pittsburgh, PA “DESMOPHEN”XP-7059 aspartic ester diamine Bayer Corp. Pittsburgh, PA “DESMOPHEN”XP-7053 aspartic ester diamine Bayer Corp. Pittsburgh, PA “AEROSIL”A-200 silica fumed silca Degussa Corp. Ridgefield Park, NJ “AEROSIL”R-972 silica fumed silca Degussa Corp. Ridgefield Park, NJ “Ti-PURE” R706 Ti02 titanium dioxide Dupont Wilmington, DE Company “Ti-PURE” R 960Ti02 titanium dioxide Dupont Wilmington, DE Company “OMYACARB” 6 calciumcalcium carbonate Omya Inc. Proctor, VT carbonate “NICRON” 402 talc talcLuzenac Englewood, NJ America, Inc. 3M “SCOTHLITE” K37 glassmicrospheres Minnesota St. Paul, MN glass bubbles Mining andManufacturing Co. “DISPERBYK” 110 dispersant additive Byk-ChemieWallingford, CT dispersant USA “JEFFAMINE” D-2000 polyoxypropylene-Huntsman Austin, TX diamine diamine Corp. “HYCAR” 1300X45 amineterminated BF Goodrich Cleveland, OH diamine liquid copolymer SpecialtyChemicals “EXPANCEL” 551 DE polymeric microsphere Akzo Nobel Duluth, GAmicrosphere Isocyanate component “DESMODUR” N-100 polyisocyanate BayerCorp. Pittsburgh, PA “DESMODUR” N-3300 polyisocyanate Bayer Corp.Pittsburgh, PA

The following examples were prepared.

Parts by Weight (Weight Fraction) Example Ingredient 1 2 3 4 5 6 7 8 910 11 12 Amine Component “DESMOPHEN” XP-7109 34.48 14.06 12.97 11.65“DESMOPHEN” XP-7059 36.02 11.34 17.35 17.44 17.29 15.76 10.47 9.4 16.41“DESMOPHEN” XP-7053 37.08 13.66 20.90 21.01 20.82 19.12 12.61 11.3319.76 37.66 “AEROSIL” A-200 silica 1.38 “AEROSIL” R-972 silica 0.18 0.780.17 0.87 0.39 0.18 “Ti-PURE” R 706 Ti02 5.87 10.11 10.31 6.55 “Ti-PURE”R 960 Ti02 37.08 10.28 10.33 10.24 9.4 10.82 9.72 11.01 “OMYACARB” 6calcium 24.83 27.11 carbonate “NICRON” 402 talc 18.01 18.36 18.30 6.896.83 15.67 16.20 17.3 14.69 3M “SCOTHLITE” K37 glass 6.39 4.28 1.82 2.9113.91 13.81 11.21 7.82 0.69 bubbles “DISPERBYK” 110 dispersant 0.86“JEFFAMINE” D-2000 diamine 7.21 6.48 “HYCAR” 1300X45 diamine 7.23“EXPANCEL” 551 DE 0.84 microsphere Isocyanate component “DESMODUR” N-10027.06 31.4 29.67 30.26 30.42 28.86 25.92 “DESMODUR” N-3300 25.84 31.0127.81 30.02 27.84 Isocyanate:amine stoichiometric 0.99:1.0 1.17 1.051.05 1.05 1.05 1.05 1.05 1.05 1.05 1.05 1.05 ratio amine:isocyanatevolume ratio 2.0:1.0 2.69:1.0 2.0:1.0 2.0:1.0 2.0:1.0 3.0:1.0 3.0:1.03.0:1.0 2.0:1.0 3.0:1.0 2.0:1.0 2.80:1.0 approximate track-free time(min) 12 2 2 3 4 4 4 4 3 3 3 12 without aid of detackification by glassbeads volume percent hollow 0 27 15 7 10 37 37 31 0 24 2 22 microspheres

Coatings were prepared from Example 1 by charging the pigmented aminecomponent to one chamber and the isocyanate component to the otherchamber of a dual chamber syringe, injecting the two componentssimultaneously through a static mixing tube to mix the amine andisocyanate components, and using a doctor blade to coat the reactivemixture onto metal and glass test panels. Coatings were also applied topaper release liners and allowed to cure. The targeted thickness was0.38 mm.

Coatings were prepared from large batches (i.e., 20 liters) of Examples2 through 10 by charging the filled amine and isocyanate components tothe separate reservoir chambers of an Airtech two component sprayingsystem and spraying the coating through a Binks 43P static mix spray gunonto a pavement surface. Coatings were also spray applied to metal testpanels and paper release liners and allowed to cure. The targetthickness was 0.38 mm.

Coatings were prepared from Examples 11 and 12 by mixing the aminecomponents as specified in the pigment dispersion procedure. Thespecified amount of the amine and isocyanate components were added to amixing vessel and blended with low shear mixing. Using a doctor blade,the reactive mixture was coated onto paper release liners, metal orglass test panels. The target thickness was 0.38 mm.

For all samples, the cure profile was monitored at 30 second intervals,by drawing a tongue depressor across the sample, and by assessing fingertack. Track-free time was defined as that time where the cure hadprogressed to the point where the material no longer flowed, and hadformed a coherent film.

Testing

The following data is useful to characterize the performance, cureprofiles and durability of coatings of the invention: dry time ortrack-free time (minutes), abrasion loss (grams), and retroreflectivity(mcd/m²/lx) performance of markings having the retroreflective opticalelements.

Abrasion resistance of the coatings can be measured using a TaberAbraser. Samples of Example 7 coated on aluminum test panels wereweighed and then abraded for 2000 cycles with a 500 g load using a CS-17abrader wheel at ambient laboratory conditions. Wear debris was wipedfrom the samples after abrasion and the samples were weighed again.Average weight loss in grams was 0.0472 compared to a loss of 0.112grams for a commercially available water-based traffic paint.

Pavements markings of the type disclosed in this invention are used todefine lanes and therefore applied as continuous lines on the edge of alane or in dashed lines separating lanes, referred to as skips. Thesemarkings are referred to as longitundinal markings in that they runparallel to the direction of travel. In actual use a relatively smallpercent of vehicles using the road will actually traverse thesemarkings.

In order to study the wear properties of a traffic marking it is commonto apply the material to a road surface in a transverse pattern, thatis, applied across the lanes and perpendicular to the direction oftravel. In that way each vehicle will hit some portion of the test line.The wear pattern that is created may be further described as “wheeltrack” or the portion of the line directly in the path of the vehicletire that receives the highest wear, or “edge line”, the area nearer theboundary of the lane that is less frequently hit. By an analysis of theperformance of a test marking applied in this manner it is possible tostudy the wear properties of a marking in an accelerated time frame toprovide an estimate of actual durability.

A test of this type was installed comparing the performance of thesubject marking to two commercially available pavement marking products.These were chosen as controls or reference materials as they are knownto provide excellent durability and more than 2 years of service life aslongitudinal markings. The data reported is reflectivity measuredaccording to ASTM E 1710-95a and taken in the wheel track, or the areaof highest wear. As can be seen from the table the subject materialcompared quite favorably with the commercial products in spite of thelower coating thickness.

Material Coating Reflectivity in mcd/m2/1x Identification thickness (mm)Initial 1 month 4 month 7 month 3M type A340 Tape 1.02 mm 530 448 248162 Patterned polyester >1 mm 390 X  183* 124 Example #8 0.254 mm 1050472 177 344 Example #8 0.254 mm 1000 450 247 254 Example #8 0.381 mm 980533 281 245 *measurement taken at 3 months

Samples 1 through 10 were applied as described above and evaluated. Thehighest durability (defined as retained anchorage to the substrates) wasobtained using those formulations containing a high loading of hollowglass bubbles/microspheres. For example, Example 6 containing 37 volumepercent glass bubbles performed better than Example 5, which is based onthe same coreactants, but contains only 10 volume percent glass bubbles.Also, Example 10, containing 24 volume percent glass bubbles, exhibitsbetter durability when compared to Example 9, which incorporatesidentical coreactants, but contains no glass bubbles. Furthermore, the“JEFFAMINE” coreactant in Examples 9 and 10, and the “HYCAR” amineterminated copolymer both increased the flexibility and tear resistanceof the coatings generated. Also, amine selection can impact coatingdurability. Example 8 exhibits better durability compared to Example 2.In this instance, the higher modulus film formed in Example 8, using thestiffer XP-7053 and XP-7059 aspartic ester amine components, is found toimpart improved durability performance, when compared to Example 2,which is based on the more flexible XP-7109 amine. The addition of thedispersant in Example 8 lowers viscosity and improves shelf stability ofthe filled amine component.

In actual use, markings based on Examples 2 and 8 have been applied at−8 C. and the coating was found to cure with track free times of lessthan 5 minutes.

All patents, patent documents, and publications cited herein areincorporated by reference as if individually incorporated. The foregoingdetailed description has been given for clarity of understanding only.No unnecessary limitations are to be understood therefrom. The inventionis not limited to the exact details shown and described, for variationsobvious to one skilled in the art will be included within the inventiondefined by the claims.

What is claimed is:
 1. A pavement marking comprising: a binder havingpolyurea groups, wherein the binder is prepared from a coatingcomposition comprising: one or more aliphatic secondary amines; one ormore polyisocyanates; material selected from the group consisting offillers, extenders, pigments, and combinations thereof; and reflectiveelements; wherein the coating composition has a minimum applicationtemperature of at least about 7° C.
 2. A pavement marking comprising: abinder having polyurea groups, wherein the binder is prepared from acoating composition comprising: one or more aliphatic secondary amines;one or more polyisocyanates; material selected from the group consistingof fillers, extenders, pigments, and combinations thereof; andreflective elements; wherein the coating composition has a track-freetime of no greater than about 5 minutes.
 3. A pavement markingcomprising: a binder having polyurea groups, wherein the binder isprepared from a coating composition comprising: one or more aliphaticsecondary amines; one or more polyisocyanates; material selected fromthe group consisting of fillers, extenders, pigments, and combinationsthereof; and reflective elements; wherein the pavement marking has anopen time of at least 30 seconds and a retained reflectivity of at least100 mcd/m²/lux after at least 2 years in use as longitudinal trafficmarkings as measured according to ASTM E 1710-95.
 4. A pavement markingcomprising: a binder having polyurea groups, wherein the binder isprepared from a coating composition comprising: one or more aliphaticsecondary amines; one or more polyisocyanates; material selected fromthe group consisting of fillers, extenders, pigments, and combinationsthereof; and reflective elements; wherein the coating has an open timeof at least 30 seconds and a minimum application temperature of at leastabout 7° C.
 5. A pavement marking comprising: a binder having polyureagroups, wherein the binder is prepared from a coating compositioncomprising: one or more aliphatic secondary amines; one or morepolyisocyanates; material selected from the group consisting of fillers,extenders, pigments, and combinations thereof; and reflective elements;wherein the coating has an open time of at least 30 seconds and atrack-free time of no greater than about 5 minutes.
 6. A pavementmarking comprising: a binder having polyurea groups, wherein the binderis prepared from a coating composition comprising: one or more aliphaticsecondary amines; one or more polyisocyanates; material selected fromthe group consisting of fillers, extenders, pigments, and combinationsthereof; and reflective elements; wherein the coating has a minimumapplication temperature of at least about 7° C. and a retainedreflectivity of at least 100 mcd/m²/lux after at least 2 years in use aslongitudinal traffic markings as measured according to ASTM E 1710-95.7. A pavement marking comprising: a binder having polyurea groups,wherein the binder is prepared from a coating composition comprising:one or more aliphatic secondary amines; one or more polyisocyanates;material selected from the group consisting of fillers, extenders,pigments, and combinations thereof; and reflective elements; wherein thecoating has a track-free time of no greater than about 5 minutes and aretained reflectivity of at least 100 mcd/m²/lux after at least 2 yearsin use as longitudinal traffic markings as measured according to ASTM E1710-95.
 8. A pavement marking comprising: a binder having polyureagroups, wherein the binder is prepared from a coating compositioncomprising: one or more aliphatic secondary amines comprising anaspartic ester amine; one or more polyisocyanates; material selectedfrom the group consisting of fillers, extenders, pigments, andcombinations thereof; and reflective elements; wherein a retainedreflectivity of at least 100 mcd/m²/lux after at least 2 years in use aslongitudinal traffic markings as measured according to ASTM E 1710-95.9. A pavement marking comprising: a binder having polyurea groups,wherein the binder is prepared from a coating composition comprising oneor more aliphatic secondary amines comprising an aspartic ester amine;one or more polyisocyanates; material selected from the group consistingof fillers, extenders, pigments, and combinations thereof; andreflective elements; wherein the coating has a minimum applicationtemperature of at least about 7° C.
 10. A pavement marking comprising: abinder having polyurea groups, wherein the binder is prepared from acoating composition comprising one or more aliphatic secondary aminescomprising an aspartic ester amine; one or more polyisocyanates;material selected from the group consisting of fillers, extenders,pigments, and combinations thereof; and reflective elements; wherein thecoating has a track-free time of no greater than about 5 minutes.